Quote:
Originally Posted by whunter
I will inspect it again asap, four years since last checked.
I am looking at replacement this year, increasing heating capacity to 125,000 btu.
The old Lennox unit never has been adequate under -10° F.
Note:
Please don't suggests sealing / insulating the house better, the walls are R-30, attic is R-60, floor is R-19, foundation crawl space walls R-13, windows are twenty year old thermal double pane.
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House exposed to a lot of winds? Possible distribution issues rather than heat generation capacity? Efficiency of the old furnace would be less than a new one today anyways. Perhaps in a very big way.
Insulation does not do much good if substantial penetration by wind is occurring. The gentleman previous posting may know something about those early furnace efficiencies in comparison to todays.
Back approximately 40 years ago when your furnace was new. If it was that long ago. Natural gas was generally cheap. No reason for a manufacturer like lennox to give great efficiency then.
The last new gas furnace our son in law installed looked loaded with computer type driven functions. It actually surprised me how complex it seemed. When they get down to only needing a plastic pipe through the wall outlet they have to be efficient.
Well if the detectors are not firing off it sounds like no breeches exist yet and that is a good thing. A shakey fan switch or one not set right will seriously waste heat. Plus 125,000 btu is a a lot of capacity up to about 2500 square feet floor area in a house as well insulated as yours usually.
That's is if the ductwork is not choking it off . There are simple ductwork guides on the internet that do not require a lot of math calculation. A quick separation test is to read the plenum temperature with a spot heat gun. It should dip and stay lower after the fan starts. If it rises further I would assume the ductwork is inadequate for the furnace output. Or the fan is too weak.Then too much heat is going up the flue.